Starting an engine with a fuel that includes alcohol may be difficult at lower temperatures because it may be difficult to vaporize the alcohol and facilitate combustion. One way to improve vaporization of a fuel that includes alcohol is to heat the fuel before the fuel is injected to the engine. However, it may be difficult to provide enough heat to the fuel in a timely manner such that the fuel vaporizes when injected to a cylinder. Specifically, it may be difficult to heat fuel to a temperature that allows vaporization of the fuel in the time between combustion events. Therefore, it may be desirable to provide a way to start an engine with a fuel that includes alcohol that does not include heating the fuel.
The inventors herein have recognized the above-mentioned limitations and have developed a method of starting an engine, comprising: substantially closing a port throttle of a cylinder; and injecting at least a portion of an amount of fuel to a cylinder during a cylinder cycle while the port throttle is substantially closed, the amount of fuel injected being during an interval that includes a middle position which is substantially aligned with a predetermined vacuum level of the cylinder.
By closing a cylinder port throttle and creating vacuum in a cylinder, it may be possible to improve starting an engine with a fuel that includes alcohol. Specifically, a cylinder port throttle may be closed during an intake stroke of a cylinder so that a vacuum level is provided in the cylinder that is greater than a vacuum in the cylinder when the cylinder is not port throttled. Further, fuel may be injected to the cylinder when vacuum within the cylinder is at a high level to improve fuel vaporization. In one example, fuel is injected at a timing that is substantially symmetric about a predetermined vacuum level. The predetermined vacuum level may be a maximum vacuum level of the cylinder during the cylinder's present cycle. In some examples, the maximum vacuum level during the cylinder cycle may be estimated from a position of the engine. In this way, fuel injection timing is coordinated with cylinder port throttle position and piston position to improve fuel vaporization and engine starting.
The present description may provide several advantages. In particular, the approach may provide more robust engine starting at lower engine temperatures. In addition, the method may reduce engine starting emissions by improving fuel vaporization and starting. For example, improved fuel vaporization may reduce engine misfires during starting and thereby reduce hydrocarbon emissions. Additionally, the approach may be more cost effective as compared to other approaches since cylinder port throttles may be used for purposes other than engine starting. For example, port throttles may be useful for providing vacuum when intake manifold pressure is high.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.